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<h1><a name="SQL-DROPCAST"></a>DROP CAST</h1>
<div class="REFNAMEDIV"><a name="AEN50438"></a><h2>名称</h2>DROP CAST&nbsp;--&nbsp;删除一个类型转换</div>
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<div class="REFSYNOPSISDIV"><a name="AEN50443"></a><h2>语法</h2>
<pre class="SYNOPSIS">DROP CAST [ IF EXISTS ] (<tt class="REPLACEABLE"><i>sourcetype</i></tt> AS <tt class="REPLACEABLE"><i>targettype</i></tt>) [ CASCADE | RESTRICT ]</pre>
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<div class="REFSECT1"><a name="SQL-DROPCAST-DESCRIPTION"></a><h2>描述</h2>
<p><tt class="COMMAND">DROP CAST</tt> 删除一个先前定义过的类型转换。</p>
<p>要能删除一个类型转换，你必须拥有源或者目的数据类型。这是和创建一个类型转换相同的权限。</p>
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<div class="REFSECT1"><a name="AEN50452"></a><h2>参数</h2>
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<dt><tt class="LITERAL">IF EXISTS</tt></dt>
<dd><p>如果指定的转换不存在，那么发出一个 notice 而不是抛出一个错误。</p></dd>
<dt><tt class="REPLACEABLE"><i>sourcetype</i></tt></dt>
<dd><p>类型转换里的源数据类型</p></dd>
<dt><tt class="REPLACEABLE"><i>targettype</i></tt></dt>
<dd><p>类型转换里的目标数据类型</p></dd>
<dt><tt class="LITERAL">CASCADE</tt><br><tt class="LITERAL">RESTRICT</tt></dt>
<dd><p>这些键字没有任何效果，因为在类型转换上没有依赖关系。</p></dd>
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<div class="REFSECT1"><a name="SQL-DROPCAST-EXAMPLES"></a><h2>例子</h2>
<p>删除从 <tt class="TYPE">text</tt> 到 <tt class="TYPE">int</tt> 的转换：</p>
<pre class="PROGRAMLISTING">DROP CAST (text AS int);</pre>
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<div class="REFSECT1"><a name="SQL-DROPCAST-COMPAT"></a><h2>兼容性</h2>
<p><tt class="COMMAND">DROP CAST</tt> 遵循 SQL 标准。</p>
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<div class="REFSECT1"><a name="AEN50487"></a><h2>又见</h2><a href="sql-createcast.html"><i>CREATE CAST</i></a></div>
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